1. Field of the Invention
The present invention relates to photothermographic materials and image forming methods.
2. Description of the Related Art
Reduction of waste solutions to be treated has been strongly desired in recent years in the medical field from the viewpoints of environmental protection and space saving. Under such circumstances, there have been needs for technologies on photosensitive photothermographic photographic materials for medical diagnosis and photography which can be exposed to light efficiently with a laser image setter or a laser imager, and can form a clear black image having high resolution and sharpness. With these photosensitive photothermographic photographic materials, it is possible to supply to customers a heat development treatment system which has eliminated the necessity of using solvent system processing chemicals, and is simpler and does not impair the environment.
The similar requirements also exist in the field of general image forming materials. However, the image for medical use is required to have a high image quality excellent in sharpness and graininess, because fine details of the image are required. In addition, the medical image is characterized by that a cold tone of an image is preferred from the viewpoint of ease of medical diagnosis. Currently, various hard copy systems utilizing pigments or dyes such as inkjet printers and apparatuses for electrophotography are prevailing as general image forming systems. However, there is no system which is satisfactory as a medical image-output system.
A thermal image formation system utilizing an organic silver salt is described in a large number of documents. In particular, the photothermographic material generally has an image-forming layer in which a catalytically active amount of a photocatalyst (e.g., silver halide), a reducing agent, a reducible silver salt (e.g., organic silver salt), and, if required, a toning agent for controlling the color tone of silver are dispersed in a binder matrix. The photothermographic materials are, after being imagewise exposed, heated to a high temperature (for example, to 80° C. or higher) to form black silver images through the oxidation-reduction reaction between the silver halide or the reducible silver salt (which functions as an oxidizing agent) and the reducing agent therein. The oxidation-reduction reaction is accelerated by the catalytic action of the latent image of the silver halide generated through exposure. For this reason, the black silver images are formed in the exposed areas. Fuji Medical Dry Imager FM-DP L has been distributed as a medical image formation system using a photothermographic material.
In photothermographic materials, substances have been used for lubricating the photothermographic materials, for improving the transferability in the production process, and for improving handling property when stacked. Examples of such substances are liquid slipping agents such as liquid paraffin disclosed in Japanese Patent Application Laid-Open (JP-A) No. 10-69023 and silicone oil disclosed in JP-A No. 2001-5138, and solid esters such as carnauba waxes disclosed in JP-A Nos. 2000-112062 and 2001-5137. These “slipping agents” are used preferably in a surface protective layer on the image-forming layer side or in a surface protective layer on the back side, particularly preferably in an outermost layer. However, the outermost layer directly contacts conveying devices, and the added substance cause transfer defects and adversely affects the output image. Accordingly, it is an important issue to find out an appropriate slipping agent. Therefore, there have been needs for improved slipping agents and photothermographic materials containing the improved slipping agents.